This invention relates to a substrate for printed wiring boards. More particularly this invention relates to a metal-laminated board or substrate for wiring boards, which is overlaid with a lead frame. Still more particularly this invention relates to he aforesaid substrates made of carbonaceous material and having excellent heat conductivity.
Conventionally, a printed circuit board forming printed wiring thereon has been generally produced by use of photolithography, namely drawing a wiring pattern on the so-called metal-clad laminated board made by cover a substrate with metal foil such as copper foil by using photo resist and etching the desired wiring pattern thereon. The printed circuit boards thus produced have been used as wiring substrates for various electrical and electronic apparatuses. Forming of the printed circuit board using the substrate laminated with metal is suited to a microscopic processing for forming a very small wiring pattern with ease. Thus, this microscopic technique makes it possible to produce a printed circuit board having very small wiring. In general, a substrate made of synthetic resin such as phenol plastic has been widely used as the metal-clad laminated board, by way of example.
Further, in general wiring board substrates overlaid with the so-called lead frame punched out from a metal plate such as of copper have been applied to various electric and electronic apparatuses. The wiring board substrate overlaid with the aforesaid lead frame (hereinafter, simply referred to as xe2x80x9clead-frame laminated substrate) is inferior in productivity to a metal-clad electric wiring boards Thus, the lead-frame laminated substrate is inferior in fine machinability in forming wiring patterns, but easy to manufacture, so that the wiring board can be produced at a low cost. Besides, the lead frame made as thick as required for the purpose can advantageously withstand high electric current, consequently to produce the wiring board having low electrical resistance loss with ease. The lead-frame laminated substrate and the metal-clad electric wiring board are respectively used for each purpose, taking into consideration various conditions such as the merit, demerit and object required for the electric wiring board and various conditions required for electric or electronic apparatus to which the electric wiring board is applied. A lead-frame laminated substrate made from a plastic board such as of phenol plastic has been widely used so far.
In general, a circuit formed on the electric wiring board or lead-frame laminated substrate generates heat has danger of causing unexpected trouble due to intense heat accumulated, though varying with the type of the components for forming the circuit. Accordingly, the electric wiring board is required to release the heat quickly. However, both the electric wiring board made from the metal-clad laminated substrate of the conventional plastic board and the lead-frame laminated substrate using the conventional plastic board entail are disadvantageous in that they are inferior in heat conductivity, and therefore, cannot meet the demand for releasing the heat.
An object of the present invention is to provide a metal-clad laminated board having excellent heat conductivity so as to form a printed circuit board capable of releasing generated heat quickly and a lead-frame laminated substrate having excellent heat conductivity so that the heat generated can be released quickly.
The inventor of the invention completed this invention upon close and diligent investigation in order to attain the object described above. According to the invention, there is provided a metal-clad laminated substrate or lead-frame laminated board for forming a printed circuit board, which is produced by using a carbon-base substrate made of carbonaceous material having an excellent heat conductivity and an insulating bonding layer for steadily joining metal-foil or lead frame to the carbon-base substrate.
Namely, in order to attain the aforementioned object of the present invention, there is provided a metal-plated laminated board for a wiring board characterized in that the carbon-base substrate is overlaid with the metal foil or lead frame through an insulating bonding layer.